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Introduction Mucinous tubular and spindle cell carcinoma is a rare subtype of renal cell carcinoma. Little is known regarding the efficacy of systemic therapy on its metastatic form because of its rarity. Case presentation We present the case of a patient with metastatic mucinous tubular and spindle cell carcinoma who achieved durable complete remission of multiple osseous metastases after undergoing cytoreductive nephrectomy followed by combination immunotherapy (ipilimumab plus nivolumab). Immunohistochemical analyses of the primary tumor revealed the presence of the tumor‐infiltrating immune cells, including activated CD8+ T cells and PD‐L1 expression, suggesting an immunologically hot tumor. Conclusion Combination immunotherapy was a viable treatment option for this disease. Immunohistochemical analyses of the tumor‐infiltrating immune cells predicted the efficacy of immune checkpoint inhibitors against rare renal cancers.